Q. Four moles of $PCl_{5}$ are heated in a closed $4\ dm^{3}$ container to reach equilibrium at 400 K. at equilibrium 50% of $PCl_{5}$ is dissociated. What is the value of $K_{c}$ for the dissociation of $PCl_{5}$ into $PCl_{3}$ and $Cl_{2}$ at 400 K?
A) 0.50
B) 1.00
C) 1.15
D) 0.05
Explanation
(a)
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ PCl_{5} \rightleftharpoons PCl_{3} + Cl_{2}$
Initial conc. $\frac{4}{4}$ 0 0
Equili. conc. $\frac{2}{4}\ \ \ \ \ \ \ \ \ \ \frac{2}{4}\ \ \ \ \ \ \ \ \ \ \frac{2}{4}$
$K = \frac{\left\lbrack PCl_{3} \right\rbrack\left\lbrack Cl_{2} \right\rbrack}{\left\lbrack PCl_{5} \right\rbrack}$
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ = \frac{2 \times 2 \times 4}{4 \times 4 \times 2} = \frac{1}{2} = 0.5$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.